This invention relates to electrophotographic reproduction using thin transparent electrophotographic film wherein the photoconductor layer of the film is imaged using a suitable light conducting optical system. Generally, such electrophotographic systems include apparatus for developing latent electrostatic images by contacting the imaged film with an electrophoretic developer or "toner". The electrostatic image is generated in the film by applying to the photoconductor layer of the film a uniform electrostatic charge and exposing the charged surface to an imaging monochromatic light pattern which causes the charges to be dissipated in the illuminated areas of the film.
Electrophotographic apparatus conventionally employs a corona charging system which electrostatically charges the photoconductive layer of the film. For imaging the film is then exposed to monochromatic light from a suitable imaging device spaced from the film such as by a lens, mirror or the like. Usually the film is moved past a corona charging unit and thereafter an imaging unit and finally through a developing station which usually takes the form of a toning head in which the developer liquid contacts the film and the latent images are developed into visual images. Additional stations may be provided for "fixing" the toned image, or if desired, transferring the image from the transparent film to another substrate such as paper. While conventional electrophotography is electrically positive working in that high density images are produced where there is no light exposure, by reversal of toning techniques, electrophotography may be made negative working. In this connection, it has been found that better image quality results for scanned imagery when negative working material is used. This invention is readily adaptable for scanned imagery utilizing a galvo oscillograph, laser, so-called fax or oscillographs and/or fiberoptic CRT imaging systems, and preferably is negative working, ideally suited for this application.
Owing to the spacing of the optical system from the photoconductive surface of the film and the characteristics of the optical component found in conventional electrophotographic equipment, interference patterns are frequently caused by differences in the path lengths of light reflected at the interface of the air and photoconductive layer and at the interface between the photoconductive layer and base layer of the film. Since variations on the order of one-quarter wavelength can cause differences of exposure, elimination of this undesirable characteristic by coating the film is not feasible. Such interference patterns which often show up as a series of darkened lines or bands obscure and/or otherwise detract from the desired image and are, therefore, most undesirable.
It is a principal object of the present invention to provide an electrophotographic apparatus which overcomes the deficiencies of the prior art.
It is another object of the present invention to provide an electrophotographic apparatus wherein interference patterns from reflections off the surfaces of the photoconductive layer of the film are minimized.
It is a further object of this invention to provide apparatus of the above type which while overcoming the problem of interference patterns is also uniquely adapted for use with scanned imagery.
It is yet another object of the present invention to provide an electrophotographic apparatus which is adaptable for electrostatic charging and imaging using an integral component.
It is also an object of the present invention to provide an electrophotographic apparatus which is compact in size and effective in operation.